In light microscopy, the specimen located on a slide is often covered with a thin flat piece of transparent material (hereinafter simply referred to as “coverslip”) before it is imaged by the microscope objective. For imaging purposes, preferably, an immersion medium is applied to the coverslip, and an objective known as immersion objective is used, the front lens of which is immersed in the immersion medium. This provides a higher numerical aperture, and thus a higher resolution. The imaging of the specimen by the microscope objective is influenced by the coverslip located in the imaging beam path according to the thickness thereof. Therefore, high-quality so-called “coverslip-corrected” microscope objectives frequently have an adjusting device which enables a lens unit provided for this purpose in the objective lens system to be adjusted along the optical axis according to the thickness of the coverslip being used, and to do so in such a way that the thickness of the coverslip is accurately taken into account in the optical imaging process, making it possible to obtain a precise image of specimen. The adjustment of this lens unit is usually in a range of a few μm.
Such a conventional adjusting device typically includes a manually operable correction ring, which is externally accessibly mounted on the objective housing and coupled to a transmission, which converts the rotational movement manually imparted to the correction ring into a corresponding linear movement of the lens unit that is intended for coverslip thickness correction, said linear movement being along the optical axis. When coverslips of different thickness are used for covering the specimens, this manual correction must be repeated for each new coverslip thickness. This is time-consuming and complicates the use of the microscope. An example of a manually operable adjusting device for coverslip thickness correction is described in DE 10 2007 002 863 B3.
A motorized adjusting device for coverslip thickness correction is known from U.S. Pat. No. 7,593,173 B2. This adjusting device has a drive motor which is mounted on an objective turret and the drive shaft of which can be coupled as desired to any of a plurality of microscope objectives carried on the objective turret. For this purpose, each of these microscope objectives has a correction ring of the type mentioned at the outset, which can be engaged with the motor shaft. Since this known adjusting device is intended to allow coupling to various microscope objectives, it is relatively difficult to make this coupling so precise that it will allow the desired high-accuracy coverslip thickness correction to be achieved. Also, the structure for engagement and disengagement of the motor mounted on the objective turret is relatively complex. In addition, the precise adjustment of the correction ring requires considerable practice and skill of the user.